Battery system and capacity recovery method for lithium ion secondary battery

Abstract

An ECU controls a PCU to perform capacity recovery control of recovering a capacity of an assembled battery. The capacity recovery control includes a discharge mode and a capacity recovery mode. In the discharge mode, the ECU discharges the assembled battery to a predetermined overdischarge region. In the capacity recovery mode, the ECU repeatedly performs, in the overdischarge region, a voltage increase of increasing a voltage across a lithium ion secondary battery due to a stop of the discharging and a pulse discharge of discharging the lithium ion secondary battery while oscillating a discharge current.

What is claimed is: 
     
       1. A battery system comprising:
 a lithium ion secondary battery including a positive-electrode active material layer and a negative-electrode active material layer disposed with a separator therebetween; 
 a charging and discharging device configured to charge and discharge the lithium ion secondary battery; and 
 a controller configured to control the charging and discharging device to perform capacity recovery control of recovering a capacity of the lithium ion secondary battery, 
 the negative-electrode active material layer including
 a facing portion that faces the positive-electrode active material layer, and 
 a non-facing portion that does not face the positive-electrode active material layer, 
 
 the capacity recovery control including
 first control of discharging the lithium ion secondary battery to a predetermined overdischarge region, and 
 second control of repeatedly performing, in the predetermined overdischarge region,
 a voltage increase of increasing a voltage across the lithium ion secondary battery due to a stop of the discharging, and 
 a pulse discharge of discharging the lithium ion secondary battery while oscillating a discharge current. 
 
 
 
     
     
       2. The battery system according to  claim 1 , wherein the second control is performed in a range in which the voltage across the lithium ion secondary battery does not fall below a predetermined lower-limit voltage. 
     
     
       3. The battery system according to  claim 1 , wherein an oscillation frequency of the discharging current in the pulse discharge is 3 kHz to 20 kHz. 
     
     
       4. The battery system according to  claim 1 , wherein the capacity recovery control is performed under a condition that a temperature of the lithium ion secondary battery is 40° C. to 80° C. 
     
     
       5. The battery system according to  claim 1 , wherein the predetermined overdischarge region is a region in which a state of charge (SOC) of the lithium ion secondary battery is 0% or less. 
     
     
       6. A capacity recovery method for a lithium ion secondary battery,
 the lithium ion secondary battery including a positive-electrode active material layer and a negative-electrode active material layer disposed with a separator therebetween, 
 the negative-electrode active material layer including
 a facing portion that faces the positive-electrode active material layer, and 
 a non-facing portion that does not face the positive-electrode active material layer, 
 
 the capacity recovery method comprising: 
 discharging the lithium ion secondary battery to a predetermined overdischarge region; and 
 repeatedly performing, in the predetermined overdischarge region,
 a voltage increase of increasing a voltage across the lithium ion secondary battery due to a stop of the discharging, and 
 a pulse discharge of discharging the lithium ion secondary battery while oscillating a discharge current.